This invention relates to new and useful improvements in shock subs positioned in the drilling string above the drilling bit to absorb vibrations, shock or impact loading otherwise imparted to the drilling string from the drilling bit during the drilling of wells for production of crude oil, natural gas, geothermal energy, etc.
Large axial displacement drill string vibrations occur in hard formations when drilling against a non-flat surface, a non-homogeneous (hard-soft) surface or a highly fractured surface. When the drilling is carried out using a conventional tricone bit, the vibration or shock or impact loading is multiplied by a factor of three in frequency and substantial impact and vibratory forces are applied in the drill string which results in early failure of tool joints, drill collars, and other portions of the drill string.
Shock absorbers in the form of shock subs which are generally run immediately above the drill bit in a drill string were first developed more than 40 years ago and have been improved in a variety of features over the years since their original introduction. Crowell U.S. Pat. No. 1,767,350 and Archer U.S. Pat. No. 1,960,688 disclose two of the earliest forms of drill string shock absorbers which utilized an elastomeric sleeve to dampen both axial and torsional vibrations. Other U.S. Patents which disclose significant improvements on shock absorbers utilizing elastomeric springs include the following: Gill et al No. 2,025,100, Crickmer No. 2,620,165, Ortloff No. 2,740,651, Vertson No. 2,765,147, Regland No. 2,795,398, No. 3,033,011, Garrett No. 3,099,918, Crane No. 3,156,106, Hughes No. 3,257,827, Wiggins No. 3,274,798, Coulter No. 3,301,009, Hughes No. 3,306,078, Vertson No. 3,323,326, Leather et al No. 3,323,327, Haushalter No. 2,325,132, Davidescu No. 3,503,224, Zerb et al No. 3,660,990, Mason No. 3,949,150.
Another type of rotary shock absorber or shock sub utilizes a compressible fluid as the shock absorbing medium. U.S. Patents illustrating this type of shock absorber include the following: Leathers No. 3,225,566, Frocks No. 3,230,740, Harrison No. 3,350,900, Galle No. 3,382,936, Galle No. 3,746,329, Webb No. 3,998,443.
Still another type of shock absorber utilizes a helical spring as the shock absorbing member. U.S. Patents which illustrate this type of shock absorber include the following: Ponti No. 1,785,559, Reed No. 2,240,519, Allen No. 2,712,437, Warren No. 2,991,635, Blair No. 3,122,902, Karle No. 3,963,228.
Still another form of shock absorber utilizes a torsional spring as the shock absorbing member. U.S. Patents illustrating this principle include the following: Mullins No. 3,947,008, Amtsperg No. 3,939,670, Frocks No. 3,339,380. Manion No. 2,570,577 discloses the use of annular disc type plate springs as shock absorbing elements. Salvatori et al No. 3,383,126 and Falkner No. 3,406,537 disclose the use of wire mesh springs as the shock absorbing member. Garrett No. 3,254,508 and Wiggins No. 3,263,446 disclose the use of a bellows as a shock absorber.
The several forms of shock absorber disclosed in the various patents listed above each have certain deficiencies. The varous spring type shock absorbers utilize a positive drive between the housing and the mandrel of the shock absorber and thus are not capable of absorbing torsional shocks or impacts. The various shock absorbers which use elastomeric springs will absorb torsional shocks or impacts but cannot be used in high temperature operations because of the deterioration of the elastomer at high temperature. Accordingly, there has been a need for a suitable shock sub which will operate under high temperature conditions and will absorb torsional shock or vibrations as well as longitudinal and radial shocks and vibrations.